Apparatus and method for delivering gas samples

ABSTRACT

An apparatus for splitting a carrier gas stream into two controlled streams and injecting a gas sample mixture into one of the carrier gas streams for delivery to a receiving chamber. By injecting the sampling out gas into a line one end of which has a restricted opening and the other end in communication with the carrier gas stream flowing to the receiving chamber, an uninterrupted sample gas slug can be delivered to said receiving chamber.

v APPKRa'rus-Am') imam) FOR-DELIVERING as. SAMPLES Filed Feb. 12, 1970 INVENTOR. G. T. PORTER vfr A T TOR/VE Y5 United States Patent 3,557,533 APPARATUS AND METHOD FOR DELIVERING GAS SAMPLES Grady T. Porter, Bartlesville, Okla., assignorto Phillips Petroleum Company, a corporation of Delaware Filed Feb, 12, 1970, Ser. No. 10,860

Int. Cl.'B01d /08 U.S. Cl. 55-67 10 Claims ABSTRACT OF THE DISCLOSURE An apparatus for splitting a carrier gas stream into two controlled streams and injecting a gas sample mixture into one of the carrier gas streams for delivery to a receiving chamber. By injecting the sample of gas into a line one end of which has a restricted opening and the other end in communication with the carrier gas stream flowing to the receiving chamber, an uninterrupted sample gas slug can be delivered to said receiving chamber.

This invention resides in an apparatus and method for delivering a gas sample. In another aspect, this invention resides in an apparatus and method for delivering a mixture of carrier and sample gas into a receiving chamber.

Heretofore utilized gas sampling apparatus generally splits a gas sample into first and second streams with carrier gas being utilized to transport at least one of the samples into a receiving chamber column, or analyzer. In these sampling devices, mixing of the sample with carrier gas generally occurs in the conduit through which the sample gas is being driven by the carrier gas. Owing to different properties of the gas and various angles through which the gas sample flows on its pathway to the analyzer, portions of the sample gas are often diffused through the conduit and carrier gas causing interrupted spaced apart gas sample volumes to pass through the analyzer with resultant recording of widely fluctuating and different, diflicult to interpret data.

It is therefore an object of this inventionto provide an apparatus and method for delivering a substantially uninterrupted, uniform, reproducible gas sample to a receiving chamber. Another object of this invention is to provide an apparatus and method for delivering a gas sample to a receiving chamber wherein the slug of sample gas is not diffused or lengthened by injection into the carrier gas stream. Yet another object of this invention is to provide an apparatus and method for delivering a gas sample to a chromatographic analyzer wherein the volume of sample gas needed for analysis-is reduced. Other aspects, objects, and advantages of the present invention will become apparent from a study of the disclosure, the appended claims, and the drawing. I

The drawing is a diagrammatic plan viewin partial see- I tion of the apparatus of this invention.

In the drawing, a first conduit 2 has a first end 4 associated with a carrier gas reservoir 6 and a second end 8 associated with a receiving chamber 10 such as a chromatographic analyzer column for example. A second conduit 1'2 has first and second portions, I14, 16 and is connected at one end of the first portion to and in fluid communication with the first conduit 2 at 'a location between the first and seconds ends 4, 8 of said first conduit 2. All portions of the first portion 14 of the second conduit 12 have a cross-sectional opening of greater area than the area of the smallest opening 18 of the second portion 16 of the second conduit 12. In order to simplify the construction of the apparatus, it is preferred that the first portion 14 of the second conduit 12 have an opening extending therethrough that is substantially of uniform crosssectional area and that the second portion 16 of the second conduit :12 has an opening extending therethrough that is substantially of uniform cross-sectional area with a restriction, such as a choke, for example, installed within the second portion 16 thereby providing the area of smallest opening 18.

A third conduit 20 is connected at a first end 22 to and in fluid communication with the second conduit 12 at a location defining adjacent ends of the first and second portions 14, 16 of said second conduit 12. It is preferred that the volume of the second conduit 12 as measured from the location of the smallest area opening 18 of the second portion '16 of said second conduit 12 to the first conduit 2 plus the volume of the third conduit 20 should be at least 50 percent smaller than a single predetermined volume of gas that is injected into the third conduit 20 by an injection means 24 with the volume of gas being measured at the pressure of the carrier gas flowing through the first conduit 2. Byso sizingthe' conduits 2, 12, 20 and locating the third conduit 20 to define the length of a first portion 14 of the second conduit 12 and the beginning of the second portion 16, rapid injection of the gas (to be more fully described later) causes a portion of the injected gas to be delivered into the first conduit 2. To further assure the entry of injected gas into the first conduit 2 and maintain a relatively low gas injection rate, the area of the smallest opening 18 of the second portion 16 of the second conduit 12 should be at least 75 percent smaller than the area of the smallest opening of the first portion 14 of the second conduit 12.

For the delivery of relatively small volumes of sample gas to a receiving chamber 10, such as an analyzer, the apparatus of this invention can be constructed of conduit having an inside diameter not greater than 0.1 inch and lengths that are as short as conveniently possible. By so constructing the apparatus, a hypodermic syringe, for example, or like apparatus can be used to inject small volumes of gas for analysis. Since it is desirable to inject a preselected mixture of sample and carrier gas in the method of this invention, it has been found generally that conduits having inside diameters larger than .01 inch generally require injection means other than hand operated a preselected rate. The proportional rate of flow of said first and second streams is regulated by the size of the opening-of the choke 18, for example, in the second portion of the second conduit 12 and the rate at which gas is permitted to enter the analyzer 10 for example. Since H the gas intake rate varies with the receiving chamber 10 or analyzer construction, the flow rates of the first and second streams of carrier gas can best be described as a ratio one to the other. For maintaining a low back pressure exerted against the injection means during injection of the sample mixture (to be later described) it is preferred that thefirst stream of carrier be maintained to flow into the analyzer 10 at a rate equal to the rate of flow of the second carrier gas stream.

While the carrier gas streams are (flowing, a preselected volume of carrier gas is drawn into the third conduit 20 and into the injection means 24 which contains a predetermined volume of sample gas. The two gases are mixed within the injection means 24 by maintaining the gases in contact one with the other within the injection means for a period of time. The adequate length of time for proper mixing of the gases is a factor that depends upon the proeprties of each of the gases and can be determined by one skilled in the art.

The carrier and sample gas mixture is thereafter injected through the third conduit 20 at a rate suflicient to cause a portion of said mixture to flow into the first conduit for subsequent transportation of a slug of the carrier and sample mixture by the carrier gas flowing from the reservoir 6 to the receiving chamber 10. The rate of injection and volume of sample gas mixture must be at values sufliciently high as to assure that a desired volume of gas mixture enters the first conduit. Knowing the volumes of the conduits of the apparatus and the rate of carrier gas flow discharging from the second conduit 12, one skilled in the art can easily calculate a desired volume and injection rate for the gas sample. Since the pressure within the second conduit 12 affects the force required to inject the sample mixture into the apparatus, the orifice size of choke 18 and the volume of carrier gas discharging from the reservoir 6 should be maintained at values such that the pressure opposing sample injection is a low value and does not require consideration when selecting the type of injection means 24 to be utilized.

It has been found that this apparatus and method are particularly useful for injecting a sample gas and helium carrier gas into a chromatographic analyzer. An example of the apparatus for chromatographic analysis is as follows:

Flow rate of first carrier gas stream 6 milliliters per minute. Flow rate of second carrier gas stream, 6 milliliters per minute.

Volume of gas sample 50 milliliters. Approximate injection rate of gas mixture 2.1 sec.

By the use of the apparatus of this example, a substantially uninterrupted uniform, reproducible gas sample mixture of known proportions was delivered to a chromatographic analyzer. Since the gas sample arrived at the analyzer in the form of an uninterrupted slug, data obtained from the analyzer was more distinct and easier to interpret.

Other modifications and alterations of this invention will become apparent to those skilled in the art from the foregoing discussion, example, and the accompanying drawing, and it should be understood that this invention is not to be unduly limited thereto.

What is claimed is:

1. An apparatus for injecting a volume of sample gas into a receiving chamber, comprising:

a first conduit having a first end adapted to be associated with a carrier gas reservoir and a second end adapted to be associated with a receiving chamber;

a second conduit having first and second portions and being connected at an end of the first portion to an end in communication with the first conduit at a location between the first and second ends of the first conduit, all portions of said first portion of the second conduit having a cross-sectional opening of greater 4 area than the area of the smallest opening of the second portion of the second conduit;

a third conduit having a first and second end being connected at the first end to and in communication with the second conduit at a location defining adjacent ends of the first and second portions of said second conduit; and

means for intermittently withdrawing and injecting predetermined volumes of gas from and into the second end of the third conduit.

2. An apparatus, as set forth in claim 1, wherein the volume of the second conduit as measured from the location of the smallest area opening of the second portion of said second conduit to the first conduit plus the volume of the third conduit is at least 50 percent smaller than a single predetermined volume of gas that is injected into the third conduit by said injection means with said volume of gas being measured at the pressure of the carrier gas flowing through the first conduit.

3. An apparatus, as set forth in claim 1, wherein the area of. the smallest opening of the second portion of the second conduit is smaller than the area of the smallest opening of the first portion of the second conduit.

4. An apparatus, as set forth in claim 1, wherein the area of the opening of the first portion of the second conduit is substantially constant throughout its length, a restriction is formed within the opening of the second portion of the second conduit, and the area of the opening of the second portion of the second conduit over the length of said second portion from the third conduit to the restriction is substantially constant.

5. An apparatus as set forth in claim 1, wherein the inside diameter of the largest conduit is not greater than .01 inch.

6. An apparatus as set forth in claim 5, wherein the means for withdrawing and injecting gas is a syringe.

7. A method for passing a volume of sample gas into a receiving chamber, comprising:

passing a stream of carrier gas into a first conduit at a preselected rate;

dividing the stream of carrier gas into first and second streams, said first stream flowing to the receiving chamber and said second stream flowing into a second conduit;

discharging gas from the second conduit at a preselected rate;

withdrawing a preselected volume of carrier gas from the second conduit;

mixing the withdrawn gas with a preselected volume of sample .gas; and

discharging the carrier and sample gas mixture into the second conduit at a rate suflicient to cause a portion of said mixture to flow into the first conduit for transportation by the carrier gas to the receiving chamber.

8. A method, as set forth in claim 7, wherein the gas is helium.

9. A method, as set forth in claim 7, wherein the rate of gas flowing in the first stream is about equal to the rate of gas flowing in the second stream.

10. A method, as set forth in claim 7, wherein the receiving chamber is a chromatographic analyzer.

References Cited UNITED STATES PATENTS 3,156,546 11/1964 Jones 55-67 3,352,089 11/1967 Modell et al. 5567 3,496,702 2/1970 Carel et al. 55-67 3,498,027 3/1970 Buchtel 55197 J. L. DECESARE, Primary Examiner 

